Wireless cellular communication networks incorporate a number of mobile UEs and a number of NodeBs. A NodeB is generally a fixed station, and may also be called a base transceiver system (BTS), an access point (AP), a base station (BS), or some other equivalent terminology. As improvements of networks are made, the NodeB functionality evolves, so a NodeB is sometimes also referred to as an evolved NodeB (eNodeB or eNB). In general, eNodeB hardware, when deployed, is fixed and stationary, while the UE hardware is portable.
In contrast to eNodeB, the mobile UE can comprise portable hardware. User equipment (UE), also commonly referred to as a terminal or a mobile station, may be fixed or mobile device and may be a wireless device, a cellular phone, a personal digital assistant (PDA), a wireless modem card, and so on. Uplink communication (UL) refers to a communication from the mobile UE to the eNodeB, whereas downlink (DL) refers to communication from the eNodeB to the mobile UE. Each eNodeB contains radio frequency transmitter(s) and the receiver(s) used to communicate directly with the mobiles, which move freely around it. Similarly, each mobile UE contains radio frequency transmitter(s) and the receiver(s) used to communicate directly with the eNodeB. In cellular networks, the mobiles cannot communicate directly with each other but have to communicate with the eNodeB.
To support dynamic scheduling and multiple-input multiple-output (MIMO) transmission in downlink (DL), several control information feedback bits must be transmitted in uplink. For example, MIMO related feedback information includes: Index of a selected precoding matrix (PMI); transmission rank indicator (RI), which corresponds to the number of useful spatial transmission layers; and the recommended/supportable modulation and coding schemes (MCS). MCS feedback is an index that is associated with a certain channel coding rate value and modulation scheme (e.g. QPSK, 16QAM, 64QAM). Note that PMI is needed only for closed-loop spatial multiplexing where channel dependent precoding is employed. For open-loop spatial multiplexing, only MCS and RI are applicable.
Control information feedback bits are transmitted, for example, in the uplink (UL), for several purposes. For instance, Downlink Hybrid Automatic Repeat ReQuest (HARQ) requires at least one bit of ACK/NACK transmitted in the uplink, indicating successful or failed cyclic redundancy check(s) (CRC). Moreover, a one bit scheduling request indicator (SRI) is transmitted in uplink, when UE has new data arrival for transmission in uplink. Furthermore, an indicator of downlink channel quality (CQI) needs to be transmitted in the uplink to support mobile UE scheduling in the downlink. While CQI may be transmitted based on a periodic or triggered mechanism, the ACK/NACK needs to be transmitted in a timely manner to support the HARQ operation. Note that ACK/NACK is sometimes denoted as ACKNAK, or any other equivalent term. Here, ACK refers to acknowledgement (successful CRC check) and NACK refers to negative-acknowledgement (failed CRC check). This uplink control information is typically transmitted using the physical uplink control channel (PUCCH), as defined by the 3GPP working groups (WG), for evolved universal terrestrial radio access (E-UTRA). The E-UTRA is sometimes also referred to as 3GPP long-term evolution (3GPP LTE). The structure of the PUCCH is designed to provide sufficiently high transmission reliability.
In addition to PUCCH, the E-UTRA standard also defines a physical uplink shared channel (PUSCH), intended for transmission of uplink user data. The Physical Uplink Shared Channel (PUSCH) can be dynamically scheduled. This means that time-frequency resources of PUSCH are re-allocated every sub-frame. This (re)allocation is communicated to the mobile UE using the Physical Downlink Control Channel (PDCCH). Alternatively, resources of the PUSCH can be allocated semi-statically, via the mechanism of semi-persistent scheduling. Thus, any given time-frequency PUSCH resource can possibly be used by any mobile UE, depending on the scheduler allocation. Physical Uplink Control Channel (PUCCH) is different than the PUSCH, and the PUCCH is used for transmission of uplink control information (UCI). Frequency resources which are allocated for PUCCH are found at the two extreme edges of the uplink frequency spectrum. In contrast, frequency resources which are used for PUSCH are in between. Since PUSCH is designed for transmission of user data, re-transmissions are possible, and PUSCH is expected to be generally scheduled with less stand-alone sub-frame reliability than PUCCH. Coded and data bits are multiplexed onto modulation symbols, which are mapped to different resource elements (RE), where an RE is defined as the smallest granularity of a time-frequency resource. A resource block (RB) is defined as the aggregation of several REs. The general operations of the physical channels are described in the E-UTRA specifications, for example: “3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA); Physical Channels and Modulation (TS36.211, Release 8).”
The uplink control information is transmitted on PUCCH, if there is no concurrent transmission of data in the uplink, as defined by 3GPP E-UTRA. In addition, 3GPP E-UTRA defines that in case both uplink control information and data need to be transmitted in the same uplink subframe, the uplink control information shall be transmitted on the allocated PUSCH resources, together with data.
A reference signal (RS) is a pre-defined signal, pre-known to both transmitter and receiver. The RS can generally be thought of as deterministic from the perspective of both transmitter and receiver. The RS is typically transmitted in order for the receiver to estimate the signal propagation medium. This process is also known as “channel estimation.” Thus, an RS can be transmitted to facilitate channel estimation. Upon deriving channel estimates, these estimates are used for demodulation of transmitted information. This type of RS is sometimes referred to as De-Modulation RS or DM RS. Note that RS can also be transmitted for other purposes, such as channel sounding (SRS), synchronization, or any other purpose. Also note that Reference Signal (RS) can be sometimes called the pilot signal, or the training signal, or any other equivalent term.
Turbo codes are a class of high-performance error correction codes developed in 1993 which are finding use in deep space satellite communications and other applications where designers seek to achieve maximal information transfer over a limited-bandwidth communication link in the presence of data-corrupting noise. The channel coding scheme for transport blocks in LTE is Turbo Coding with a coding rate of R=⅓, using two 8-state constituent encoders and a contention-free quadratic permutation polynomial (QPP) turbo code internal interleaver. Trellis termination is used for the turbo coding. Before the turbo coding, transport blocks are segmented into byte aligned segments with a maximum information block size of 6144 bits. Error detection is supported by the use of 24 bit CRC. The ⅓ coding rate triples the bit-count for transmission of the block. The general operations of channel coding are described in the E-UTRA specifications, for example: “3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA); Multiplexing and channel coding (TS36.212, Release 8).” Convolutional codes are also used in 3GPP E-UTRA for downlink and uplink control channels.